This project is designed to extend the basic passive probe technology to make the probes more versatile by giving them more ways to interact with the cells which surround them. We have developed and successfully implemented a process which allows the inclusion of chemical delivery channels on the same substrate as the conductive electrode sites. This permits multipoint drug delivery and multichannel recording and/or stimulation with minimal tissue disruption. Successful packaging techniques for the chemical delivery probes have been developed which permit handling and use in the normal context of acute pharmacological characterization of neuronal activity. In vitro tests have verified the passage of quantified doses of fluid to a surrounding medium. In vivo tests of simultaneous chemical delivery and extracellular recordings in guinea pig inferior and superior colliculus are demonstrating results consistent with conventional approaches. Data presented at meetings including that of the 1998 Association for Research in Otolaryngology has generated much interest in the device by the neuroscience community. New devices have been fabricated which have configurations relevant to specific neurophysiological studies to be carried out in Dr. Bledsoe's laboratory. Developments during the past year include the development of an in-line flowmeter for monitoring of the dose chemical delivered.